Storage Unit Sizes Explained: How to Pick the Right Size for Your Stuff
Most people choosing self storage for the first time get the size wrong in one of two directions: they either pay for months of empty air, or they discover on moving day that the mattress will not go in unless the lounge is stood on its end. This storage unit sizes guide takes the usual ladder of locker, small, medium and large and translates it into the household contents you actually own, then gives you a way to sense-check your choice against how often you will need to get back in.
One caveat worth setting up front: every size recommendation is an estimate, including the ones here. Two households with the same number of bedrooms can need very different units, because one has dismantled the bed frames and applied smart packing tips to save space by packing into uniform cartons while the other is storing a three-seater lounge, a fridge and a tool chest that will not stack with anything.
The four size bands at a glance
Rather than memorising a chart of measurements, think of self storage as four steps on a ladder. A locker is for boxes and compact items only, a small unit handles roughly one room or studio-style overflow, a medium unit covers the contents of a small apartment or several rooms, and a large unit is for the multi-room or whole-home contents that come out of a bigger move.
It helps to think in the terms you will use on the day: moving cartons, a queen mattress, a fridge and washing machine, camping and fishing gear, a swag and tubs from a FIFO stint, or the half a house that comes out of a kitchen during a renovation. Those are the items that decide your size, not square metres. Matching the right unit to these everyday items is central to making a downsize work, and the ladder is a starting point for your enquiry rather than a booking guarantee, since exact dimensions, ceiling height and access arrangements vary from site to site.
What fits in a locker, small, medium or large unit
A locker suits reduced-height storage, so think archive and document boxes, luggage, camping gear, seasonal clothing, hand tools, a few small sports items and the personal effects you want out of the house. What it will not take is a room of furniture, so if a mattress or a wardrobe is on your list, step up a band.
A small unit is the one-room option: a bedroom set packed well, meaning a mattress, bedside tables, a small desk, a couple of chairs, a stack of cartons and perhaps a small appliance. It is the usual choice for short-term overflow while a room is being renovated or while you are between houses.
A medium unit holds the contents of a small apartment or several rooms, which typically means lounge furniture, a dining setting, bedroom furniture, a fridge or washing machine and a decent run of cartons, plus the awkward pieces that refuse to stack neatly, such as a bike, a pram or a floor lamp.
A large unit is for multi-room or whole-home contents: multiple bedroom settings, lounge and dining furniture, whitegoods, outdoor furniture, many cartons and the bulky items a bigger move always produces, like a tool chest, a kayak or a trampoline frame.
Be careful with box counts in particular. Thirty uniform cartons stack into a tidy, stable block, whereas thirty assorted tubs, bags and reused supermarket boxes can take up half as much space again, and fragile items need breathing room too, which eats into usable volume.
A four-step way to decide what size you need
Start with a written inventory, room by room: bedrooms, lounge, kitchen, laundry, study, garage, shed and the outdoor areas. The garage and shed are where people most often miss something bulky, and a wheelbarrow or a ride-on mower will change your answer.
Next, sort that list into four groups: cartons, stackable furniture, non-stackable furniture, and awkward pieces. The awkward group is the one that drives your size, because it includes mattresses, the fridge, the washing machine, lounges, bikes, tool chests and outdoor equipment, none of which can be reshaped to suit the space.
Then estimate cartons based on what you will have after packing, not on how many cupboards you are emptying. It is also worth checking whether some of it can stay home, because a half-empty wardrobe or an unused corner of the garage can drop you a whole band.
Finally, use your largest and least flexible items to rule out the bands that are clearly too small, then pick the smallest remaining band that fits the inventory plus any space you need to move around. If you will be opening the unit regularly, plan a centre or side aisle and keep frequently needed items near the door; if it is going to be sealed until move-out day, a tighter pack is reasonable.
When to save money and when to size up
A smaller unit is genuinely enough when the storage period is short, most of your contents are uniform cartons, the furniture has been dismantled, there is little that is fragile and you have no reason to reach anything before move-out. Under those conditions you can pack floor to ceiling and the space works hard for you.
Size up when any of these apply: you will be in and out regularly, you are storing fragile or valuable items that should not be crushed under a load, you have a bulky lounge or odd-shaped furniture, you are storing whitegoods alongside everything else, or you expect to add more later, which is common during a staged move or a renovation that runs long.
The cost argument cuts both ways, because the cheapest unit stops being the best value the moment it forces unsafe stacking, blocks access to the items you need, or means transferring everything into a larger unit after you have already carried it in once. A narrow walkway costs you a bit of floor area and saves you the time and damage of unloading half the unit to reach one box.
Packing choices that change how much actually fits
How you pack can move you a whole band up or down, so decide your packing approach before you commit to a size. Dismantle bed frames, tables and shelving wherever you can, and tape the hardware to the item itself or keep it all in one clearly labelled parts box so reassembly is not a treasure hunt.
Use strong cartons of a consistent size. Uniform boxes stack squarely and let you plan the space in blocks, whereas a mix of bags, open tubs and odd containers creates gaps you cannot use and stacks that lean. Build upwards where it is safe, with heavy boxes on the floor, lighter ones on top, and fragile items protected and placed so they are never carrying a load.
Two items deserve particular care. Mattresses can be stored upright only if they are properly covered and supported so they do not bow or slump against something sharp, and whitegoods should be cleaned and fully dried before they go in, with doors left slightly ajar where appropriate so moisture and odours do not build up. These are among the simplest tips for stress-free furniture storage to follow, yet they make the biggest difference when it comes time to unpack.
Lastly, pack for the future you: put anything you might need first near the front, and label boxes on at least two sides so the contents are still readable once they are stacked in a wall.
Confirm dimensions and availability before you commit
Once you have your room-by-room list and a likely band, the next step is a quick conversation rather than another online calculator. Contact Adlam Transport to confirm current unit dimensions, access arrangements and what is actually free, because availability of secure self storage units in Karratha moves around and the closest real match beats a generic size chart every time.
Make the enquiry easy to answer by leading with the specifics: how many rooms you are storing, your rough carton count, whether there are mattresses, whitegoods or a lounge involved, any outdoor or work gear, how long you expect to store, and whether you need to get in and out during that period. Those details let someone point you to the right unit in one go.
The rule to carry into that conversation is simple. Choose the smallest unit your contents comfortably fit into, and allow extra space when access, fragile items or awkward furniture are part of the picture, because paying a little more for a unit you can walk into is usually cheaper than moving twice.